This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-298630, filed Sep. 27, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a perpendicular magnetic recording/reading apparatus using a perpendicular magnetic recording method which is expected as a high-density recording technique, and a magnetic recording medium used in this perpendicular magnetic recording/reading apparatus.
2. Description of the Related Art
Compared to a longitudinal magnetic recording layer, a perpendicular magnetic recording layer can perform high-density linear recording even with a large recording layer thickness and has a thermal decay resistance higher than that of a longitudinal magnetic recording layer. In particular, a perpendicular two-layered film medium having a high-permeability soft magnetic layer below a recording layer having perpendicular magnetic anisotropy makes ideal perpendicular recording possible by the interaction between a head and the soft magnetic layer. This can further increase the recording density. However, if this soft magnetic layer is formed in a recording medium, magnetization in the soft magnetic layer readily changes during disk rotation even with weak external magnetization. This lowers a recording signal or produces noise.
To improve this change in the magnetization of a soft magnetic layer, Jpn. Pat. Appln. KOKAI Publication No. 7-129946, for example, discloses a magnetization fixing layer for a backing layer which is formed between a soft magnetic backing layer and a substrate and which forms exchange coupling with the soft magnetic layer and has uniform magnetization. However, if a larger external magnetic field, such as that of a voice coil motor for head position control, is applied to a magnetic recording/reading apparatus, the magnetization directions in the magnetization fixing layer for a backing layer and the soft magnetic layer cannot be the same. This makes magnetization in the soft magnetic layer unstable.
It is an object of the present invention to provide a magnetic recording/reading apparatus capable of reducing noise by stabilizing magnetic domains in a soft magnetic backing layer during recording and reproduction.
According to a first aspect of the invention, there is provided a perpendicular magnetic recording/reading apparatus comprising a perpendicular magnetic recording medium having a nonmagnetic substrate, and a magnetization fixing layer for a backing layer, soft magnetic backing layer, and perpendicular magnetic recording layer formed in the above order on the nonmagnetic substrate,
wherein a maximum external magnetic field of a magnetic recording medium longitudinal component which is applied to the perpendicular magnetic recording medium is smaller than an absolute value Hn of a magnetic field at an intersection of a straight line connecting two points of an M-H curve in the longitudinal direction of the soft magnetic backing layer and a tangent of the M-H curve, one of the two points being a point (Hs, Ms) at which magnetization saturates in the first quadrant, the other of the two points being a positive intersection (0, Mr) of the M-H curve and the ordinate, and the tangent being at a negative intersection (xe2x88x92Hc, 0) of the M-H curve and the abscissa.
According to a second aspect of the invention, there is provided a perpendicular magnetic recording/reading apparatus comprising a perpendicular magnetic recording medium having a nonmagnetic substrate, and a magnetization fixing layer for a backing layer, soft magnetic backing layer, and perpendicular magnetic recording layer formed in the order named on the nonmagnetic substrate,
wherein the perpendicular magnetic recording medium has a recording area in which magnetization directions in the magnetization fixing layer for a backing layer and the soft magnetic backing layer are the same direction owing to an exchange coupling interaction, and a non-recording area in which the magnetization directions are not the same direction.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.